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    <title>Document</title>
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    <script>
         console.log(NaN,typeof NaN);
         console.log(0 / 0,6 / 0,-6 / 0);
         console.log(Math.sqrt(-1));
         console.log("abc" - 10);
         console.log(undefined + 10);
         console.log(parseInt("hello"));
        const a = 0/0;
        const b = parseInt("hello");
        console.log(a == b);
        if(number.isNaN(parseInt("hello"))){
            console.log("不是一个数字，不能继续计算");
        } 
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